Pathological or not, ensuring that pathnames can essentially contain any byte value except the 0 terminator, and it will still work, is important to prevent surprising behaviour which often has security implications.
The only character not allowed in Unix file names is the forward slash directory separator, so even that would be a pathological mistake waiting to bite someone.
Edit: my mistake, they can't contain nulls either: https://news.ycombinator.com/item?id=8485861